Hi, I just bought Bioshock infinite today but my computer cannot handle it, lags real hard during fighting sequences, and shuts down randomly, so I am looking to get a new graphics card.

I am currently using Geforce 550ti, i5 2500k @3.3ghz cpu, my motherboard is
GIGABYTE GA-P67A-UD3-B3: it says it support for ATI CrossFireX.

My budget for new video card is around 300 USD , so I narrowed it down to these two after following tom's hardware best bang for the buck gfx card guide.

XFX Radeon HD 7950 vs SAPPHIRE Radeon HD 7950;
They are the same price on newegg, but I don't know if they are necessarily the same, one has Boost Clock with lower core clock, and I am not familiar with overclocking things.

Btw, should I get newer graphics card opposed to these that had been released for a while?

I've had good luck with Sapphire. different models will have two verses one fan from either manufacturer...just a matter if you like to exhaust out of the case, or prefer a little quieter fan with more exhaust inside the case....personal preference...very little difference in price...varies by sales that day.

Yeah, no really new models to consider...a little stagnant right now....still the best bang for the buck.